This invention relates to molded reinforced cement structures, and particularly to ferro-cement boat and other marine structures.
Ferro-cement (a rich concrete mortar highly reinforced with steel wire and rods) is used in building boats by means of open mold plastering and by male and female molding. In the open mold plastering, the desired shape of marine structure is formed by building appropriate frames which are then covered with wire mesh and rod reinforcement to form an armature that is wire tied; the compact armature is plastered with a rich dry cement recipe and finished from the outside. This open mold plastering method requires considerable care in the formation of a soundly structured shape and in the tying of the armature. The plastering also requires considerable hand labor, and the application of protective or cosmetic finishes is difficult.
In male molding, the reinforcing wire and rod are attached to the male mold, usually by staples, and the mold is built in inverted form which is destroyed after plastering, and the plaster is finished smooth from the outside with some difficulty. Because of the destruction of the male mold, it is appropriate more for one-of-a-kind construction but not for mass production.
Female molding is described in the Iorns U.S. Pat. No. 3,652,755 in which successive layers of cementitious material are applied to a female mold with the reinforcing metal being pressed into the second and successive layers. This method is difficult to use because the reinforcement cannot be uniformly and evenly dispersed as well as compacted and joined.
The female mold process is also described in the Mattingly U.S. Pat. No. 3,705,228: In a fiberglass mold, an unreinforced outer resinous coat is applied, to which coat chicken-wire mesh is attached by means of an epoxy adhesive; part of the mesh projects from the adhesive so that tying wires may be joined thereto and used for tying down the ferro-cement reinforcement armature. The process described in this patent requires the adhering of the metal chicken wire to an outer skin of epoxy resin which would be brittle and weak in tension. The chicken wire would be difficult to form to curved or flat surfaces, and it would be difficult to thread tying wires to the projected portions of the chicken-wire mesh as well as to align the armature wires and rods thereto.
Ferro-cement, as used herein, calls for a "specific surface ratio" of the area of the armature wire used as reinforcement to the volume of the cement composite; where this ratio is between about 2 and 3 cm..sup.-1, the material is generally considered to be ferro-cement, while a ratio below 0.5 cm..sup.-1 indicates reinforced concrete.